import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param pHead1 ListNode类
     * @param pHead2 ListNode类
     * @return ListNode类
     */
    //ONT4 合并两个排序的链表
    public ListNode Merge (ListNode pHead1, ListNode pHead2) {
        // write code here
        ListNode newH = new ListNode(-1);
        ListNode tmp = newH;

        while(pHead1 != null && pHead2 != null){
            if(pHead1.val < pHead2.val){
                tmp.next = pHead1;
                pHead1 = pHead1.next;
                tmp = tmp.next;
            }else{
                tmp.next = pHead2;
                pHead2 = pHead2.next;
                tmp = tmp.next;
            }
        }
        if(pHead1 == null){
            tmp.next = pHead2;
        }
        if(pHead2 == null){
            tmp.next = pHead1;
        }
        return newH.next;
    }

    //ONT5 反转链表
    public ListNode ReverseList (ListNode head) {
        // write code here
        if(head == null){
            return null;
        }
        ListNode cur = head.next;
        head.next = null;
        while(cur != null){
            ListNode curN = cur.next;
            cur.next = head;
            head = cur;
            cur = curN;
        }
        return head;
    }

    //ONT1 链表内指定区间反转
    public ListNode reverseBetween (ListNode head, int m, int n) {
        // write code here
        if(head == null || head.next == null || m == n){
            return head;
        }
        ListNode dummy = new ListNode(-1);
        dummy.next = head;

        ListNode pre = dummy;
        for(int i=1;i<m;i++){
            pre = pre.next;
        }
        ListNode start = pre.next;
        ListNode then = start.next;

        for(int i=0;i<n-m;i++){
            start.next = then.next;
            then.next = pre.next;
            pre.next = then;
            then = start.next;
        }
        return dummy.next;
    }
}
